WIP on loading files from disk

kernel/bpb.asm

@@ -0,0 +1,16 @@
+; IN	DL	drive number
+;	BP	ptr to bpb_size'd buffer
+bpb_load:
+  mov [bp+(bpb_size-1)], dl
+
+  xor dx, dx
+  xor ax, ax
+  call drive_read
+
+  mov si, (diskbuf+0x0B)
+  mov di, bp
+  mov cx, (bpb_size-1)
+  rep movsb
+
+  ret
+

kernel/config.asm

@@ -1,20 +0,0 @@
-config_tokens:
-.buffers:
-  db 8, "BUFFERS="
-.drives:
-  db 7, "DRIVES="
-.files:
-  db 6, "FILES="
-.none:
-  db 0
-
-config_parse_int:
-  ret
-
-; IN	BX	offset to config data
-config_first_run:
-  mov si, bx
-  mov di, config_tokens
-  call string_search_token
-  int3
-  ret

kernel/drive.asm

@@ -0,0 +1,48 @@
+; Load a sector from drive.
+; IN    DX:AX   sector number
+;	BP	ptr to BPB
+drive_read:
+  push ax
+  push cx
+  push dx
+  push bx
+  push si
+
+  mov cx, dx
+  or cx, ax
+  jz .fast
+
+  div word [bp+13] ; ax:temp     = (lba / spt)
+  inc dx           ; dx:sector   = (lba % spt) + 1
+  mov cl, dl       ; sector number
+
+  div word [bp+15] ; ax:cylinder = (tmp / heads)
+                   ; dx:head     = (tmp % heads)
+  mov ch, al       ; cylinder number
+  mov dh, dl       ; head number
+  mov si, 5        ; retry count
+.try:
+  mov dl, [bp+(bpb_size-1)] ; drive number
+  mov bx, diskbuf
+  mov ax, 0x0201
+  int 0x13
+.giveup:
+  pop si
+  pop bx
+  pop dx
+  pop cx
+  pop ax
+  ret
+.fast: ; fast lane for boot sector
+  inc cl
+  jmp .try
+.fail:
+  ; reset disk
+  mov ah, 0x00
+  int 0x13
+  ; loop with si
+  dec si
+  test si, si
+  jnz .try
+  stc
+  jmp .giveup

kernel/exec.asm

@@ -3,12 +3,12 @@ exec_chain:
   mov si, 0x81
 exec:
   push bx
-  sub sp, 36
+  sub sp, fcb_size
   mov bx, sp
 
   call fcb_parse
-  call fcb_print
+  call fcb_open
 
-  add sp, 36
+  add sp, fcb_size
   pop bx
   ret

kernel/fcb.asm

@@ -2,11 +2,11 @@
 ; IN	SI	ptr to filename
 ;       BX	ptr to FCB
 fcb_parse:
-  push si
   push di
   push ax
   mov di, bx
-  inc di
+  xor ax, ax
+  stosb
 .cleanout:
   push di
   mov cx, 0x0A
@@ -38,31 +38,33 @@ fcb_parse:
   je .eret
   ret
 .eret:
+  dec si
   pop ax
 .ret:
   pop ax
   pop di
-  pop si
   ret
 
-; Print a FCB (for debugging)
-; IN	BX	ptr FCB
-fcb_print:
-  push dx
-  push cx
-  push si
-  mov si, bx
-  inc si
-  mov cx, 11
-.loop:
-  lodsb
-  mov dl, al
-  call putc
-  loop .loop
-  mov dl, 0x26
-  call putc
-.ret:
-  pop si
-  pop cx
-  pop dx
+fcb_open:
+  cmp byte [bx], 0
+  jne .drivedone
+  mov al, default_drive
+  inc al
+  mov [bx], al
+.drivedone:
+  push bp
+  sub sp, bpb_size
+  mov bp, sp
+
+  mov dl, [bx]
+  dec dl
+
+  call bpb_load
+  mov ax, [bp]
+  mov cx, [bp+2]
+  mov dx, [bp+4]
+  mov bx, [bp+6]
+
+  add sp, bpb_size
+  pop bp
   ret

kernel/main.asm

@@ -6,15 +6,16 @@ cpu 8086
 ; A single sector for disk i/o
 %define diskbuf (self-0x200)
 
-; BYTE sectors/track and BYTE number of sides
-; 4 times for A: B: C: and D:
-%define chstab  (diskbuf - (4*2))
-
 ; DWORD partition offset for C: and D:
-%define parttab (chstab - (2*4))
+%define parttab (diskbuf - (2*4))
 
 %define stack   (parttab)
 
+%define default_drive BYTE [0x5B]
+
+%define fcb_size 16
+%define bpb_size 18
+
 org self
 jmp init
 
@@ -69,3 +70,5 @@ putc:
 
 %include "exec.asm"
 %include "fcb.asm"
+%include "bpb.asm"
+%include "drive.asm"